Electronic assemblies used in two-way radios and other electronic devices which emit or are used in the vicinity of radio frequency and electromagnetic radiation require a means of thermal dissipation and sometimes require shielding from electromagnetic and radio frequency interference (EMI and RFI). One such assembly is the radio frequency power amplifier (RF PA) module. Various RF PA module assemblies are in use today.
One example of a prior art RF PA module assembly includes a PA module having straight leads hand soldered to a printed circuit board (pcb). An opening in the pcb is used for the body of the module. A flange is coupled to the PA module and mates with a heat sink, such as a radio chassis, either directly or with a thermal interface, such as a thin pad or grease, and is fastened to the chassis with screws. This assembly provides thermal dissipation from the module to the heat sink, however no shielding is provided.
Another example of a known RF PA module assembly includes having the PA module mounted upside-down and fastened with screws to a one or two piece bracket. The bracket is hand soldered to a pcb. The leads of the PA module are either bent so that the bottom edge of the leads is flush with the pcb or the leads are inserted into thru holes and extend through the pcb. In both cases the leads are hand soldered. A flange is coupled to the RF PA module and mates with the heat sink either directly or with a thermal interface, such as a thin pad or grease, providing thermal dissipation. Here again, no shielding is provided.
Products incorporating the PA module configurations described above typically use separate shielding apparatus such as cans or fences with pop off tops in order to minimize the emissions emanating from the PA module assembly. However, these shields are typically located around the module pcb and do not enclose the entire module or the leads. While this type of shielding may provide sufficient protection for some EMI/RFI standards, such as FCC, it is inadequate for other standards, such as ETSI. Designers are faced with many challenges in obtaining optimal thermal dissipation for the PA module to run efficiently and optimal shielding of PA module to meet the EMI/RFI United States and international standards. The prior art assemblies do not provide adequate shielding of the PA module and therefore may not meet all of the EMI/RFI standards. The prior art assemblies fail to provide a robust design with adequate tolerances. As such, dynamic movement under mechanical environments may apply stress to the leads of the module causing shearing of the leads or cracks in the solder joints. All of these problems are exacerbated when designing for the tight space requirements of portable communication devices.
Accordingly, a need exists for a power amplifier module assembly that overcomes the noted problems of thermal dissipation and shielding.